The present invention relates to a diagnosis of abnormality of an operation of a sensor, and more particularly to the realization of the diagnosis of abnormality with the simple constitution without using dedicated parts or the like.
For example, an electronic control unit for an internal combustion engine of an automobile which is represented by a diesel engine includes various sensors, and detection signals of the sensors are used for an operation control of the internal combustion engine.
As one of these sensors, a pressure sensor for detecting a rail pressure in a common-rail-type fuel injection control device is important in realizing the proper fuel injection, and various proposals have been made for detecting abnormality or a malfunction of the pressure sensor.
As one of diagnoses of a malfunction of the pressure sensor in such a common-rail-type fuel injection control device, for example, there has been proposed the following method or the like where, in performing a diagnosis of a malfunction of the pressure sensor, an instruction of intentionally increasing a rail pressure is given, and also an instruction of decreasing an energizing time of injectors is given and, eventually, when it is determined that there is no change in a fuel injection amount so that there is no change in exhaust gas characteristics, it is estimated that there is no malfunction in the pressure sensor (see patent document 1, for example).
However, in the above-mentioned malfunction diagnosis method, for detecting the malfunction of the pressure sensor, it is necessary to make the unnecessary instruction of increasing a rail pressure irrelevant to the fuel injection which is an original purpose, and this instruction brings about not only the redundancy in a control operation but also an undesired actual increase of the rail pressure. There is a possibility that the increase of the rail pressure will influence a fuel injection operation.
As a measure to surely detect abnormality or a malfunction of the sensor while avoiding such a drawback, for example, there has been proposed a method where two pressure sensors are provided, and a malfunction of a pressure sensor is detected by comparing outputs of two pressure sensors. However, it is necessary to provide two pressure sensors which are expensive. Hence, device cost is increased and the method is not always realistic as a result.